DE 36 02 477 A1 shows, as an example, a camshaft having a cavity that extends centrally through the camshaft, and the camshaft has a radial bore, so that oil can be transported between the cavity and the outside of the camshaft. In this regard, the oil transport to the outside of the camshaft serves for lubrication of slide bearings, by way of which the camshaft is accommodated in a cylinder head so as to rotate.
From DE 10 2005 014 680 A1, an adjustable camshaft having a phase shifter is known, and at least two oil connections are known for activation of the phase shifter, by way of which connections pressure oil can be applied to the phase shifter for activation. In order to apply oil to the phase shifter, a pressure connection must be transferred from a resting component to the rotating camshaft, because the phase shifter rotates along with the camshaft. The first main bearing of the adjustable camshaft, which borders on the phase shifter, is frequently used to apply pressure with oil, and pressure oil is transferred to the rotating camshaft by way of an inner bearing shell, which rotates along with the outer shaft of the camshaft by way of circumferential grooves. In this regard, radial bores are provided between circumferential grooves in the bearing shell, into which radial bores open, which extend through the bearing shell, the outer shaft, and the inner shaft, and the radial bore in the inner shaft opens into the cavity in the inner shaft.
A further example of an adjustable camshaft with oil transfer from a resting bearing shell to a phase shifter that rotates with the camshaft is known from EP 2 527 607 A2. The inner shaft and the outer shaft have radial openings, wherein the openings in the outer shaft must have an elongated expanse facing in the circumferential direction, in order to allow coverage of the radial opening in the inner shaft with the radial opening in the outer shaft by way of an adjustment angle of the inner shaft in the outer shaft. However, it is disadvantageous that as a result, the outer shaft is significantly weakened.
If the inner shaft and/or the outer shaft has/have a circumferential groove, so that the fluid connection between the radial opening in the inner shaft and the radial opening in the outer shaft takes place by way of the circumferential groove, it is true that coverage of the radial openings is not required, but the mechanical ability of the outer shaft and/or that of the inner shaft to withstand stress is weakened by the circumferential groove. In particular, the weakening adds up when the grooves are provided along with elongated openings that extend in the circumference direction, so that the strength of the camshaft can reach critical lower limits.
To guarantee oil flow even in boundary positions of the angle adjustment of the inner shaft in the outer shaft, it is necessary to create an elongated expanse, in the circumferential direction, of the opening in the outer shaft, so that even in the end angle positions of the rotated inner shaft in the outer shaft, essentially complete coverage of the radial openings in the inner shaft and the outer shaft is guaranteed. Depending on a required rotation range of the inner shaft in the outer shaft, over an angle of rotation, the first radial openings must be structured to be very long in the circumference direction of the outer shaft, thereby resulting in significant weakening of the camshaft.